Support deterministic output for bootimg/filesystem
Adding salt to bootimg/filesystem so that avbtool can produce the same
output with same input.
Adding timestamp/uuid to filesystem so that resulting image can be
deterministic.
Bug: 229784558
Test: m com.android.virt
# remove intermediates and touch some sources
m com.android.virt
# compare two built artifacts
Change-Id: I4e4668fd0ac42a35bea5a33ec3ae8c362b6a6bd2
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index ccf9e9d..6e1e78a 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -15,7 +15,9 @@
package filesystem
import (
+ "crypto/sha256"
"fmt"
+ "io"
"path/filepath"
"strings"
@@ -88,6 +90,13 @@
// Symbolic links to be created under root with "ln -sf <target> <name>".
Symlinks []symlinkDefinition
+
+ // Seconds since unix epoch to override timestamps of file entries
+ Fake_timestamp *string
+
+ // When set, passed to mkuserimg_mke2fs --mke2fs_uuid & --mke2fs_hash_seed.
+ // Otherwise, they'll be set as random which might cause indeterministic build output.
+ Uuid *string
}
// android_filesystem packages a set of modules and their transitive dependencies into a filesystem
@@ -276,6 +285,11 @@
return fcBin.OutputPath
}
+// Calculates avb_salt from entry list (sorted) for deterministic output.
+func (f *filesystem) salt() string {
+ return sha1sum(f.entries)
+}
+
func (f *filesystem) buildPropFile(ctx android.ModuleContext) (propFile android.OutputPath, toolDeps android.Paths) {
type prop struct {
name string
@@ -321,12 +335,19 @@
addStr("avb_add_hashtree_footer_args", "--do_not_generate_fec")
partitionName := proptools.StringDefault(f.properties.Partition_name, f.Name())
addStr("partition_name", partitionName)
+ addStr("avb_salt", f.salt())
}
if proptools.String(f.properties.File_contexts) != "" {
addPath("selinux_fc", f.buildFileContexts(ctx))
}
-
+ if timestamp := proptools.String(f.properties.Fake_timestamp); timestamp != "" {
+ addStr("timestamp", timestamp)
+ }
+ if uuid := proptools.String(f.properties.Uuid); uuid != "" {
+ addStr("uuid", uuid)
+ addStr("hash_seed", uuid)
+ }
propFile = android.PathForModuleOut(ctx, "prop").OutputPath
builder := android.NewRuleBuilder(pctx, ctx)
builder.Command().Text("rm").Flag("-rf").Output(propFile)
@@ -451,3 +472,11 @@
}
return specs
}
+
+func sha1sum(values []string) string {
+ h := sha256.New()
+ for _, value := range values {
+ io.WriteString(h, value)
+ }
+ return fmt.Sprintf("%x", h.Sum(nil))
+}
